Security film system with reactive adhesives

ABSTRACT

Proposed is a security film system for documents or in general data carriers having a transfer layer and an adhesive or gluing layer portion which has at least one micro-encapsulated reactive adhesive component, wherein the adhesive or gluing layer portion remains activatable over a period of time of up to at least one year and the at least one reactive adhesive component hardens after activation to form a duromer.

[0001] The present invention concerns a security film system fordocuments or in general data carriers with a transfer layer and anadhesive or gluing layer portion.

[0002] Security film systems of that kind are wide-spread and are usedin the form of hot stamping films or protective laminate films in themost widely varying areas.

[0003] Irrespective of their area of use, whether as a security elementfor banknotes, check or credit cards or for identity documents, thesecurity film systems known from the state of the art are generally of asubstantially identical layer structure. In that respect, hot stampingor laminate films of that kind generally have an adhesive layer portionfor fixing on a substrate, that is to say an article to be decorated orprotected. Arranged on that adhesive layer portion is a transfer layerwhich is composed of one or more layer portions and includescorresponding security elements. In that case, metallised ornon-metallised diffraction structures can be contained in the layerconstitution, wherein the individual layer portions can also be providedover the full surface area or part thereof and can be of varying colors.Frequently those layer portions are formed by differing lacquers whichare preferably applied by means of printing processes. It is possible inthat way to produce decorative patterns or security elements in accurateregister relationship. The transfer layer may further include lacquerlayer portions which can be irreversibly modified subsequently, forexample by irradiation with a laser.

[0004] Security film systems of that kind are generally known in regardto the structure of the transfer layer and were the subject of numerouspatent applications in recent times.

[0005] The specified security film systems in that case are usuallyprovided with thermoplastic adhesive systems. Those security filmsystems are transferred on to the article to be protected, for example apersonalised pass page or the like, by means of pressure andtemperature. In that procedure, the adhesive is caused to melt by meansof the action of temperature in the operation of transferring the systemon to the article. In that case the adhesive is physically anchored inthe substrate to be decorated or provided with a security element, orthe surface of the material of the substrate, and provides for thenecessary bonding adhesion after the arrangement has cooled down. Nochemical reaction takes place in that situation. A particulardisadvantage of those adhesive systems however is that they can bereversibly melted at any time and thus the transfer layer containing thesecurity element can be easily detached by heating and applied toanother substrate. Such thermoplastic bonds are thus a potentialweakness in security film systems, by virtue of the thermoplasticproperties of such bonds.

[0006] An improvement in terms of forgery-proof nature of theabove-mentioned security film systems is achieved by the use of reactiveadhesive systems which cross-link under room conditions. It is possiblein that way to produce compact composite systems which can no longer bemelted. In that case, those adhesive systems experience a change intheir chemical structure during the reaction and become a duromermaterial. They can no longer be melted or deformed by the action oftemperature. If the temperature is increased excessively the adhesivelayer portion suffers decomposition. In general the temperatures forthat to happen are above 200° C. so that it can be assumed that thecomposite system is substantially resistant to mechanical, thermal andchemical attacks and attempts at manipulation and forgery are at leastmade more difficult than with thermoplastic adhesive systems.

[0007] DE 40 22 584 discloses a series of single- or multi-componentreactive adhesives for a use of that kind. In the case of thesingle-component reactive adhesive, in accordance with the disclosure,there is an adhesive layer portion only on the hot stamping film. Thatsingle-component reactive adhesive, in accordance with DE 40 22 584,involves a masked cross-linker which is liberated under the effect ofheat and which contains for example a blocked polyisocyanate.

[0008] However that single-component reactive adhesive which is knownfrom the state of the art suffers from the disadvantage that thecross-linking reaction progresses slowly even under ambient conditionswhich usually apply, so that hot stamping films provided with asingle-component reactive adhesive of that kind only have a limitedstorage life.

[0009] In the case of the multi-component reactive adhesive which isalso known from DE 40 22 584, at least one second component isnecessarily to be provided on the substrate to be decorated. That givesrise to serious limitations in regard to the security film system or thehot stamping film as they can only be applied to substrates which have alayer with a corresponding reactive adhesive component.

[0010] WO 99/29755 discloses a process for the production of and the useof storage-stable, latently reactive layers or powders ofsurface-deactivated polyisocyanates and dispersion polymers withfunctional groups. The latently reactive products in layer or powderform, in accordance with the disclosure, serve to produce adhesive joinsand coatings, wherein gluing of films is mentioned in general terms butis not discussed in greater detail.

[0011] Therefore the object of the present invention is to provide asecurity film system which is as resistant to forgery and manipulationas possible, which is simple and economical to produce, which can beused over a prolonged period of time after manufacture and which as faras possible avoids the disadvantages known from the state of the art.

[0012] A further object of the present invention is to provide asecurity film system for documents, which is subjected to as fewlimitations as possible in respect of the substrate to be protected orthe document to be protected, and the location and/or the time ofapplication to the substrate or document respectively.

[0013] The foregoing object is attained by a security film system fordocuments having the features of claim 1.

[0014] Advantageous configurations of the invention are thesubject-matter of claims 2 through 10 and claims 12 and 13.

[0015] The present object is further attained by a process for theproduction of a security film system as set forth in claim 11.

[0016] The security film system for documents is advantageouslyparticularly flexible to handle because the steps which are effectedafter production of the transfer layer, for example the diffractive filmcomposite, up to the application of the transfer layer to a substrate ordocument, can be carried out at various locations and at various times.

[0017] In general however the adhesive or gluing layer portion isapplied directly following production of the transfer layer. Themicro-encapsulated reactive adhesive which is used in accordance withthe invention is available commercially, for example under the namePurbond HCM® from Ebnöther AG, Sempach, Switzerland. A reactive adhesiveof that kind can be handled particularly well and can be applied to thetransfer layer for example in a powder coating process at temperaturesof between about 60 and 70° C., wherein the fixing which takes place atthat temperature causes the formation of a lacquer-like adhesive orgluing layer portion which is not yet activated and which remainsactivatable over a surprisingly particularly long period of time. Theadhesive or gluing layer portion of the present security film systemremains activatable over a period of time of up to at least one year.

[0018] In that respect a particular advantage of the security filmsystem according to the invention for documents is the possibility ofdecentral document use, that is to say application of the transfer layerat a location different from the production location thereof. Incontrast to what are known as ‘online processes’ in which coating,application and hardening of the adhesive, that is to say production ofthe composite arrangement with the document to be protected, take placeat the location of manufacture of the transfer layer, the presentinvention permits much more flexible use of the security film system fordocuments.

[0019] Usually the film system having the adhesive or gluing layerportion according to the invention, that is to say the combination ofthe transfer layer and the adhesive or gluing layer portion is providedon rolls or in other desired formats which are good to handle, and takento the location of use in that fashion. The term location of use is usedin the present context to denote the location at which the security filmsystem is applied to a document or generally a substrate. In that case,the security film system according to the invention is placed andpositioned on the document or substrate and briefly raised for exampleby a rolling lamination process to an activation temperature in therange of between about 110 and 150° C. In that situation, thermalsplitting of the micro-encapsulation takes place and subsequently acorresponding cross-linking reaction in which the at least onemicro-encapsulated reacted adhesive component contained in the adhesiveor gluing layer portion reacts to form a duromer and forms a firm,practically non-releasable connection of the transfer layer to thedocument or substrate to be protected.

[0020] The micro-encapsulated reactive adhesive component is preferablythermally activatable, in which respect however there is basically alsothe possibility of using for example reactive adhesives which areactivatable by UV or X-ray radiation as long as they can be fixed in anadhesive or gluing layer and remain activatable for a sufficiently longperiod of time. Particularly preferably the at least one reactiveadhesive component is formed by a micro-encapsulated isocyanate or by amicro-encapsulated phthalic acid anhydride.

[0021] It has surprisingly been found that the adhesive or gluing layerportion in the security film system according to the invention fordocuments is easily accessible to partial activation in relation to thesurface area and partial activation in relation to the mass of the atleast one reactive adhesive component. In that respect, covering of theadhesive and gluing layer portion by means of a thermally insulatingstencil and short-term (partial) heating of the regions not covered bythe stencil is adequate for partial activation. The degree of partialpre-cross-linking can be easily predetermined by control in respect ofthe temperature and the duration of heating of the regions which are notcovered by the stencil. It is possible in that way to provide thesecurity film system according to the invention with regions involving adifferent adhesive force.

[0022] The prescribed regions involving a differing adhesive force canbe produced in that respect in any arrangement, thus for example in theform of more or less abstract patterns or in the form of alphanumericcharacters such as for example letters or serial numbers.

[0023] In a particularly preferred embodiment of the present inventionwhich is particularly suitable for decentral use the adhesive or gluinglayer portion, on the side which does not face towards the transferlayer, has a protective layer portion. That ensures that, during storageof the security film system according to the invention and/ortransportation, the adhesive layer portion does not suffer from soilingwhich can adversely affect the capability of adhesion to the document orsubstrate to be protected. A protective layer portion of that kind isformed in particular by a removable film because the protective layerportion in that form can be removed particularly easily and without anyproblem.

[0024] Particularly preferably the transfer layer of the security filmsystem according to the invention includes a diffraction layer portionor a layer portion which produces an optical diffraction pattern asoptically effective structures of that kind are accepted and establishedas a security element in many different uses and areas of use and can behandled particularly well.

[0025] In a development of the present invention, on the side which doesnot face towards the adhesive or gluing layer portion, the transferlayer has a protective layer portion. That protective layer portion canbe in the form of a fixed protective lacquer layer portion or also inthe form of a removable protective layer portion which on the one handprotects the surface of the security film system, which is latervisible, from damage during manufacture, storage and transportation. Inparticular it can also be in the form of a carrier layer portion for thesecurity film system.

[0026] In this respect it is basically to be noted that the man skilledin the art of security elements and hot stamping and decorative films isfamiliar with the basic layer structure of such film systems and thetransfer layers thereof.

[0027] In regard to the protective and/or carrier layer portion arrangedon the transfer layer, it should also be mentioned that preferablydisposed between the transfer layer and the protective and/or carrierlayer portion is a separating layer portion which facilitates thedetachment of that layer portion. In that respect, in a particularconfiguration, the separating layer portion is at the same time in theform of a protective layer portion which remains on the transfer layer.

[0028] The security film system according to the invention can be usedextremely advantageously in the form of labels or stickers. In that casethe labels or stickers can be stamped out of an extensive security filmsystem or can be provided in stamped-out form.

[0029] Using labels or stickers of that kind makes it possible toimplement simplified application to documents or substrates to besecured.

1. A security film system for documents comprising a transfer layer andan adhesive or gluing layer portion which has at least onemicro-encapsulated reactive adhesive component, wherein the adhesive orgluing layer portion remains activatable over a period of time of up toat least one year and the at least one reactive adhesive componenthardens after activation to form a duromer.
 2. A security film system asset forth in claim 1 characterised in that the at least one reactiveadhesive component is formed by a micro-encapsulated isocyanate orphthalic acid anhydride.
 3. A security film system as set forth in claim1 or claim 2 characterised in that at least one reactive adhesivecomponent is thermally activatable.
 4. A security film system as setforth in one of the preceding claims characterised in that the adhesiveor gluing layer portion has a protective layer portion on the side whichdoes not face towards the transfer layer.
 5. A security film system asset forth in claim 4 characterised in that the protective layer portionis formed by a removable film.
 6. A security film system as set forth inone of the preceding claims characterised in that the transfer layerincludes a diffraction layer portion or a layer portion which producesan optical diffraction pattern.
 7. A security film system as set forthin one of the preceding claims characterised in that the transfer layerhas a protective layer portion which is arranged on the side of thetransfer layer, which does not face towards the adhesive or gluing layerportion.
 8. A security film system as set forth in one of the precedingclaims characterised in that the transfer layer is arranged on a carrierlayer portion with the side which is in opposite relationship to theadhesive or gluing layer portion.
 9. A security film system as set forthin claim 8 characterised in that a separating layer portion is arrangedbetween the carrier layer portion and the transfer layer.
 10. A securityfilm system as set forth in claim 9 characterised in that the separatinglayer portion is at the same time in the form of a protective layerportion for the transfer layer.
 11. A process for the production of asecurity film system as set forth in one of claims 1 through 7characterised in that the adhesive or gluing layer portion is applied ina powder coating process.
 12. A security film system as set forth in oneof claims 1 through 10 characterised in that it is in the form of alabel or sticker.
 13. A security film system as set forth in claim 12characterised in that the label or sticker is in stamped-out form.